The last time we discussed machine tools, we talked about how to choose the size of the new metalworking lathe that your wallet is itching to pour itself into. The next big decision to make is “new or used?” If you’re in North America, this question has a lot of overlap with the classic question “Import or American?”. The answer boils down to what your needs are, and what you want to get out of this machine.
If you are new to machining, and want to learn the skills, I recommend starting with an Asian import machine. If you’re careful which one you select, you’ll end up with a very reasonably priced lathe that can do precise work right out of the crate. If your interest is in learning how these tools work, and in doing a restoration project, an old American machine is a great choice. Let’s look at these two routes in more detail.
The lathe is known as the King of Machine Tools for a reason. There are very few things that you can’t make with one. In fact, people love to utter the old saw that the lathe is the only machine tool that can make itself. While catchy, I think that’s a bit disingenuous. It’s more accurate to say that there are parts in all machine tools that (arguably) only a lathe can make. In that sense, the lathe is the most “fundamental” machine tool. Before you harbor dreams of self-replication, however, know that most of an early lathe would be made by hand scraping the required flat surfaces. So no, a lathe can’t make itself really, but a lathe and a skilled craftsperson with a hand-scraper sure can. In fact, if you’ve read the The Metal Lathe by David J. Gingery, you know that a lathe is instrumental in building itself while you’re still working on it.
We’re taking trip through the machining world with this series of articles. In the previous article we went over the history of machine tools. Let’s cut to the modern chase now and help some interested folks get into the world of hobby machining, shall we? As we saw last time, the first machine tools were lathes, and that’s also where you should start.
Lathes are usually used to turn metal, but internal keyways and splines are operations often performed with a broach. An older tool called a shaper would be perfect here, but shapers are relatively rare these days — or are they? There are many examples of shaper attachments for lathes. These are human-powered devices that scrape a bit of metal off each pass. The lathe itself is used to keep the workpiece in place and move the tool in a repeatable way.
Rather than create a shaper jig from scratch, [John] decided to use his compound slide as the shaper slide itself. He removed the compound slide lead screw, which allowed the compound to slide freely. He then fabricated a double hinged bar and bolted this to the compound slide. Moving the bar causes the slide to move. Just add a cutting tool, and you’re ready to cut a keyway. Add an indexing plate, and you’re ready to cut a spline. You can see the tool in action after the break.
You can get pretty much any part you need online these days, but some specialty parts are a little hard to come by. So if your needs are esoteric, like tiny hydraulic cylinders for RC snow plows, you might just have to roll your own.
To be honest, we never really knew that realistic working hydraulics on such a small scale were a thing, but [tintek33]’s video below opened our eyes to a new world of miniature mechanicals. You’d think a linear actuator would be a fine stand-in for the hydraulic ram on a tiny snow plow for an RC truck, but apparently no detail is too small to address in painstaking detail. And as with many things in life, the lathe is the way to get there. Every part is scratch-built from raw brass, aluminum and steel on a mini lathe, with the exception of a few operations that were sent over to the mill that could have been done with hand tools in a pinch. The video is longish, so if you’re not into machining you can skip to 16:40 or so and pick the action up at final assembly. The finely finished cylinder is impressively powerful when hooked up to [tintek33]’s hydraulic power pack, and looks great on the plow. He’s got some other videos on his site of the RC snow plow in action that are worth a look, too.
Becoming accomplished with a lathe is a powerful skillset, but it’s only half of the journey. Being clever comes later, and it’s the second part of the course. Patience is in there somewhere too, but let’s focus on being clever. [TimNummy] wants a knobbed bolt with critical parameters, so he makes his own. After the break, there is a sixty-second summary of the linked video.
Making stock hardware is a beginner’s tasks, so custom hardware requires ingenuity or expensive machinery. Adding finger notches to a bolthead is arbitrary with an indexing chuck, but one isn’t available. Instead, hex stock becomes a jig, and the flat sides are utilized to hold the workpiece at six intermittent angles. We can’t argue with the results which look like a part that would cost a pretty penny.
Using material found in the workshop is what being clever is all about. Hex brass stock comes with tight tolerances on the sides and angles so why not take advantage of that?
In December 2016, [Bruno M.] was lucky enough to score a 70+ year old Logan 825 lathe for free from Craigslist. But as you might expect for a piece of machinery older than 95% of the people reading this page, it wasn’t in the best of condition. He’s made plenty of progress so far, and recently started tackling some broken gears in the machine’s transmission. There’s only one problem: the broken gears have a retail price of about $80 USD each. Ouch.
On his blog, [Bruno] documents his attempts at replacing these expensive gears with 3D printed versions, which so far looks very promising. He notes that usually 3D printed gears wouldn’t survive in this sort of application, but the gears in question are actually in a relatively low-stress portion of the transmission. He does mention that he’s still considering repairing the broken gears by filling the gaps left by the missing teeth and filing new ones in, but the 3D printed gears should at least buy him some time.
As it turns out, there’s a plugin available for Fusion 360 that helpfully does all the work of creating gears for you. You just need to enter in basic details like the number of teeth, diametral pitch, pressure angle, thickness, etc. He loaded up the generated STL in Cura, and ran off a test gear on his delta printer.
Of course, it didn’t work. Desktop 3D printing is still a finicky endeavour, and [Bruno] found with a pair of digital calipers that the printed gear was about 10% larger than the desired dimensions. It would have been interesting to find out if the issue was something in the printer (such as over-extrusion) or in the Fusion 360 plugin. In any event, a quick tweak to the slicer scale factor was all it took to get a workable gear printed on the third try.
It’s becoming abundantly clear that [Colin Merkel] doesn’t know the definition of “good enough”. Not only has he recently completed his third (and most impressive) wristwatch build, but he also managed to put together one of the most ridiculously romantic gifts ever conceived. While some of us are giving our significant others a gift card to Starbucks, he made his girlfriend a watch with a chart on the face representing the position of the stars at the time and place of their first meeting.
As per his usual style, the documentation on this build is phenomenal. If paging through his gallery of build images doesn’t make you want to get a lathe and start learning metal working, nothing will. A chunk of stainless steel rod miraculously becomes a gorgeous wrist watch over the course of a few dozen images, perfectly encapsulating that old adage of “making it look easy”.
Certainly the highlight of this build is the star chart on the face. To make it, he used PyEphem to plot the position of the brightest stars that were visible at the time and place of their first meeting. He then wrote a script to take those stars and convert their positions to G-Code the CNC could use to drill holes in the appropriate locations. The depth of the hole even corresponds to the magnitude (brightness) of each star, giving the chart a subtle 3D effect.
Unfortunately, [Colin] made a couple of mistakes during this build, to the point that he’s not exactly sure how to proceed. He mentions he might even be forced to start over from scratch. It’s hard to imagine how something that looks this good could ever end up being a failure, but the world of watch making is unkind.
To start with, he used 304 stainless instead of 303. This made machining the case much more difficult, and from his very first cut he realized it was going to be a problem. While it was an annoyance he mentions a couple times during the build log, he was at least was able to work through it.
The real problem came at the end, when he put the watch together. He originally made his designs assuming a front glass which was 0.5 mm thick, but in actuality used a piece that is 0.8 mm thick. This slight difference is just enough to cause the seconds hand to rub up on the glass, putting drag on the movement. The end result is that the battery dies extremely quickly, effectively rendering the watch useless.
We can’t imagine the heartbreak [Colin] felt when he realized what happened; we felt bad just reading about it. But given his track record, we have no doubt he’ll get the issue sorted out. It would be a shame to start over completely, but there’s some consolation in knowing it’s part of the learning process: you don’t become a master of your craft without making a couple mistakes along the way.